Sage code to find left-truncatable primes in bijective numeration

bijective-truncatable-primes.py

DIGITS = "123456789X"
ENCODE = dict(( (i+1, d) for (i, d) in enumerate(DIGITS) ))
DECODE = dict(( (d, i+1) for (i, d) in enumerate(DIGITS) ))

def encode(n):
    a = []
    while n > 0:
        n, r = divmod(n, 10)
        if r == 0: n, r = n - 1, 10
        a.append(ENCODE[r])
    return "".join(reversed(a))

def decode(s):
    return reduce(lambda n, c: 10*n + DECODE[c], s, 0)

def search(s):
    if not is_prime(decode(s)): return
    print(s)
    for digit in DIGITS:
        search(digit + s)

search("3")
search("7")